Japanese Patent Laying-Open No. 10-290529 discloses an electric power unit mounted to an electric vehicle. The electric power unit includes a battery, an electric circuit system such as a running motor supplied with power from the battery and an on-vehicle auxiliary machine, an inverter circuit for generating a commercial AC voltage that converts a direct-current (DC) voltage from the battery to a commercial AC voltage for application to an external AC load, a cutoff switch provided between the inverter circuit and the external AC load, and a leakage detecting circuit that detects a ground-fault current leaking from the battery so as to detect leakage of the electric circuit system. Upon detection of the leakage, the leakage detecting circuit stops the inverter circuit and causes the cutoff switch to operate to firstly cut off the power supply to the external AC load, without interrupting the power supply to the electric circuit system such as the running motor and the on-vehicle auxiliary machine.
According to this electric power unit, when there occurs leakage in the external AC load, the power supply circuit system for the external AC load is first interrupted preferentially. Thus, occurrence of critical problems such as electric shock, deterioration of the original function of the electric vehicle and the like can be prevented quickly, without impairing the power supply to the electric circuit system in the main body of the electric vehicle including the running motor and the on-vehicle auxiliary machine.
In, the electric power unit disclosed in Japanese Patent Laying-Open No. 10-290529, the power supply circuit system for the external AC load is configured with a separate system from the electric circuit system including the running motor and the on-vehicle auxiliary machine (hereinafter, also referred to as a “main circuit system” for clear distinction from the power supply circuit system for the external AC load). That is, the electric power unit disclosed in Japanese Patent Laying-Open No. 10-290529 includes the inverter circuit for generating a commercial AC voltage separately from the inverter for driving the running motor, the on-vehicle auxiliary machine and the like. Upon detection of the leakage, only the power supply circuit system for the external AC load is shut down.
In the case where a system is to be configured to use the main circuit system for supplying power to an external AC load, instead of providing an additional inverter circuit for generating the commercial AC voltage, for the purposes of downsizing the device and reducing the cost, however, simply shutting down the inverter of the main circuit system to cut off the power supply to the external AC load upon detection of the leakage may adversely affect the operations of the running motor and/or the on-vehicle auxiliary machine in a certain operational state.
Here, although it may be conceivable to operate only the cutoff switch to stop the power supply to the external AC load, without stopping the inverter, it cannot reliably stop the output in two steps or two ways, which leads to lack of safety.
Further, in order to ensure sufficient safety with regard to the leakage, checking of operations of the leakage detecting function is required before starting the power supply to the external AC load.